Building rest client fails with "java.lang.IllegalArgumentException: <FQCN> is not an interface."

[buzaan]

Describe the bug
When testing OpenLiberty services in Java versions greater than 11, using @RESTClient-annotated classes in integration tests results in a failed test with the error message: "java.lang.IllegalArgumentException: my.package.MyService is not an interface". Re-running with Java11 results in a successful test.

To Reproduce

• git clone https://github.com/OpenLiberty/guide-microshed-testing.git (Using this as a known-working project)
• cd guide-microshed-testing/finish
• mvn verify

Expected behavior
PersonServiceIT and ErrorPathIT complete without errors.

System information:

• OS: macOS 12.1
• Java Version: 17 (tested with 15 & 18 which show this same behavior as well)
• MicroShed Testing Version: 0.9.1

Additional context
I'm not sure where I'd even begin debugging this since it really caught me by surprise. Any guidance or even just confirmation that this is indeed a bug would be helpful. Since it is working on Java11 I could fall back to that if nothing else.

For reference, here is the output of a failed run:

buzaan@buzaan ~/scratch/guide-microshed-testing/finish % git rev-parse HEAD
cda558a8cab1d2d2630b6d7463973862729a188a
buzaan@buzaan ~/scratch/guide-microshed-testing/finish % java -version
openjdk version "17.0.1" 2021-10-19
OpenJDK Runtime Environment (build 17.0.1+12-39)
OpenJDK 64-Bit Server VM (build 17.0.1+12-39, mixed mode, sharing)
buzaan@buzaan ~/scratch/guide-microshed-testing/finish % mvn verify
(...output....)
[INFO] --- maven-failsafe-plugin:2.22.0:integration-test (default) @ guide-microshed-testing ---
[INFO] 
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running io.openliberty.guides.testing.PersonServiceIT
[INFO] Found application file at: /Users/buzaan/scratch/guide-microshed-testing/finish/target/guide-microshed-testing.war
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
[INFO] Using ServerAdapter: org.testcontainers.containers.liberty.LibertyAdapter
[INFO] Using ApplicationEnvironment class: org.microshed.testing.testcontainers.config.TestcontainersConfiguration
[INFO] Starting 1 container(s) in parallel for class io.openliberty.guides.testing.PersonServiceIT
[INFO]   localhost/testcontainers/dw5vlrv2adhpyddu:latest
[ApplicationContainer] 
[INFO] ApplicationContainer[localhost/testcontainers/dw5vlrv2adhpyddu:latest] has exposed ports:
[INFO]   9080 --> 35221
[ApplicationContainer] Launching defaultServer (Open Liberty 22.0.0.11/wlp-1.0.70.cl221120221010-1540) on Eclipse OpenJ9 VM, version 1.8.0_345-b01 (en_US)
[ApplicationContainer] [AUDIT   ] CWWKE0001I: The server defaultServer has been launched.
[ApplicationContainer] [AUDIT   ] CWWKG0093A: Processing configuration drop-ins resource: /opt/ol/wlp/usr/servers/defaultServer/configDropins/defaults/keystore.xml
[ApplicationContainer] [AUDIT   ] CWWKG0093A: Processing configuration drop-ins resource: /opt/ol/wlp/usr/servers/defaultServer/configDropins/defaults/open-default-port.xml
[ApplicationContainer] [AUDIT   ] CWWKZ0058I: Monitoring dropins for applications.
[ApplicationContainer] [AUDIT   ] CWWKT0016I: Web application available (default_host): http://ab727dc296fb:9080/health/
[ApplicationContainer] [ERROR   ] CWWKZ0002E: An exception occurred while starting the application guide-microshed-testing. The exception message was: java.lang.UnsupportedClassVersionError: JVMCFRE199E bad major version 61.0 of class=io/openliberty/guides/testing/PersonServiceApp, the maximum supported major version is 52.0; offset=6
[ApplicationContainer] [AUDIT   ] CWWKF0012I: The server installed the following features: [json-1.0, mpConfig-2.0, mpHealth-3.1, mpRestClient-2.0].
[ApplicationContainer] [AUDIT   ] CWWKF0013I: The server removed the following features: [appClientSupport-1.0, appSecurity-2.0, appSecurity-3.0, batch-1.0, concurrent-1.0, distributedMap-1.0, ejb-3.2, ejbHome-3.2, ejbLite-3.2, ejbPersistentTimer-3.2, ejbRemote-3.2, j2eeManagement-1.1, jacc-1.5, jaspic-1.1, javaMail-1.6, javaee-8.0, jaxb-2.2, jaxws-2.2, jca-1.7, jcaInboundSecurity-1.0, jdbc-4.2, jms-2.0, jpa-2.2, jpaContainer-2.2, jsf-2.3, jsp-2.3, managedBeans-1.0, mdb-3.2, ssl-1.0, wasJmsClient-2.0, wasJmsSecurity-1.0, wasJmsServer-1.0, webProfile-8.0, websocket-1.1].
[ApplicationContainer] [AUDIT   ] CWWKF0011I: The defaultServer server is ready to run a smarter planet. The defaultServer server started in 12.821 seconds.
[INFO] All containers started in 16955ms
[INFO] Building rest client for class io.openliberty.guides.testing.PersonService with base path: http://localhost:35221/guide-microshed-testing/ and providers: [class org.microshed.testing.jaxrs.JsonBProvider]
Nov 08, 2022 2:46:30 PM org.apache.cxf.jaxrs.client.JAXRSClientFactoryBean createWithValues
SEVERE: java.lang.IllegalArgumentException : io.openliberty.guides.testing.PersonService is not an interface
[ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 18.151 s <<< FAILURE! - in io.openliberty.guides.testing.PersonServiceIT
[ERROR] io.openliberty.guides.testing.PersonServiceIT  Time elapsed: 18.149 s  <<< ERROR!
java.lang.IllegalArgumentException: io.openliberty.guides.testing.PersonService is not an interface

[INFO] Running io.openliberty.guides.testing.ErrorPathIT
[INFO] Using ApplicationEnvironment class: org.microshed.testing.testcontainers.config.TestcontainersConfiguration
[INFO] All containers started in 21ms
[INFO] Building rest client for class io.openliberty.guides.testing.PersonService with base path: http://localhost:35221/guide-microshed-testing/ and providers: [class org.microshed.testing.jaxrs.JsonBProvider]
Nov 08, 2022 2:46:30 PM org.apache.cxf.jaxrs.client.JAXRSClientFactoryBean createWithValues
SEVERE: java.lang.IllegalArgumentException : io.openliberty.guides.testing.PersonService is not an interface
[ERROR] Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.047 s <<< FAILURE! - in io.openliberty.guides.testing.ErrorPathIT
[ERROR] io.openliberty.guides.testing.ErrorPathIT  Time elapsed: 0.047 s  <<< ERROR!
java.lang.IllegalArgumentException: io.openliberty.guides.testing.PersonService is not an interface

[ApplicationContainer] [INFO] 
[INFO] Results:
[INFO] 
[ERROR] Errors: 
[ERROR]   ErrorPathIT » IllegalArgument io.openliberty.guides.testing.PersonService is n...
[ERROR]   PersonServiceIT » IllegalArgument io.openliberty.guides.testing.PersonService ...
[INFO] 
[ERROR] Tests run: 2, Failures: 0, Errors: 2, Skipped: 0

[buzaan]

Meant to mention – if I do create an interface for the service it will work in newer Java versions.